Epihalohydrin polymers are well known commercial elastomers which have solvent, fuel oil, ozone and heat resistance coupled with low temperature flexibility and easy formability. These elastomers offer a combination of many of the desirable properties of nitrile, polychloroprene, polysulfide, and polyacrylic rubbers.
The epihalohydrin homopolymers are generally resistant to ozone, have extremely low gas permeability, and are well suited for gaskets, oil-field specialties, diaphragms, and pump and valve parts. The epihalohydrin copolymers generally have superior low temperature flexibility for automotive and refrigeration applications such as fuel pump diaphragms, gasoline hose, and oil seals. Paper and printing rolls are other uses. Blends of the homopolymers and copolymers are useful for high temperature conveyor belts and automotive mounts and vibration isolators.
Curing or vulcanization of the epihalohydrin polymers has been a problem in the past. Complex curing systems are required to obtain the desired balance of necessary physical properties in a variety of applications. Many of these curing systems can cause mold fouling and are otherwise undesirable. A simple peroxide cure would be advantageous in many applications for vulcanizing polymers of epihalohydrins or copolymers of epihalohydrin and alkylene oxides. However, up to now, attempts to cure such polymers with organic peroxides have not been successful because the peroxide free radical attacks the ether linkage of the polymer and initiates degradation before the polymer reaches a satisfactory state of cure.
The Sartomer Company Bulletin BP-1 entitled "Basic Principles of Peroxide-Coagent Curing of Elastomers" is in point. This bulletin discloses that certain elastomers cannot be cured with peroxide-coagent systems, the common coagents being the polyfunctional polymethacrylates. Elastomers that cannot be thus cured are said to include epihalohydrin rubbers as well as polyisobutylene, butyl rubber, and polypropylene rubbers.
Oetzel U.S. Pat. No. 4,251,648 discloses compositions comprising a polymer of an epihalohydrin, an unsaturated glycidyl ether, and optionally, alkylene oxide, that are cured in the presence of an organic peroxide, an acid acceptor, and an unsaturated polyfunctional methacrylate. By the use of an unsaturated glycidyl ether, curing of the epihalohydrin polymers can be accomplished without having to resort to the use of such deleterious substances as red lead, certain barium compounds, ethylene thiourea, and the like.
U.S. patent application entitled "Epihalohydrin Cure Systems" filed on May 24, 1982 on behalf of inventor J. P. Barnhouse, is analogous to the Oetzel patent with the exception of disclosing the use of polyol polyacrylate ester coagents in place of unsaturated polyfunctional methacrylate coagents.
Japanese published patent application No. Sho 46-96750 (laid open No. Sho 48-60751), discloses a peroxide curable terpolymer composition comprising a terpolymer of epichlorohydrin, ethylene oxide, and allyl glycidyl ether together with zinc stearate, carbon black, red lead, an antioxidant, and dicumyl peroxide. This publication discloses that homopolymers of epihalohydrins and copolymers of an epihalohydrin with an alkylene oxide either decompose or produce products of very low strength after being cross-linked with an organic peroxide in presence or absence of a coagent.